1. Field of the Invention
The present invention relates to power management controller integrated circuits (ICs), and more particularly to a fault indicator system for a power management IC in which an existing pin performing a power management function is re-used to report different fault conditions using corresponding fault signatures that identify the type of protection fault.
2. Description of the Related Art
Power controller ICs or chips are typically designed to enter a shut-down protection condition in the event of several general fault conditions, such as output under-voltage, over-current and input voltage out of range. The majority of commercial power management ICs, however, usually include only one pin dedicated to indicate the fault protection or to provide a simple power status monitor, such as the power good (PGOOD) pin or the like. Because of IC pin and spacing limitations, it is disadvantageous to add another external pin to provide fault identification. The PGOOD pin is either pulled high (e.g., logic TRUE) during normal operation or pulled low (e.g., logic FALSE) during a fault condition. Otherwise, the IC provides no additional information about the particular fault condition that initiated shut-down protection or that caused the fault indication.
Knowledge of the cause of shut-down protection is useful for the designers of the power controller as well as system designers of power systems that use the power controller IC. From the system designer's point of view, whenever a shutdown happens or when the power good signal is de-asserted, the system designer needs to know the root cause of the shutdown so that the proper actions can be taken to correct the problem, such as increasing over-current threshold, increasing the output capacitor, changing the layout, etc. From the IC design point of view, knowing the exact cause of the shut-down or fault can help to diagnose whether the root cause is related to internal IC design (and thus usable to improve IC design) or whether it is a field application issue.
The debugging and probing efforts are often very time consuming when an unexpected shut-down happens, especially for those faults triggered by the probability of a combination of events. For example, it has been reported that it may take on the order of tens of hours or even days to diagnose a single shut-down event. The power management IC is usually installed on a motherboard or the like with many high-speed digital devices. Since troubleshooting measurements are relatively sensitive, the noise resulting from the digital circuits and the power conversion circuit complicates the measurement. The noise in a motherboard environment further increases the difficulty of identifying the root cause. In order to identify the root cause of the fault protection related shut-down, it is usually mandatory to measure multiple points of the circuit.
It is desired to provide more detailed fault indication information for power management or controller ICs with limited pin and spacing requirements without interfering with the function of the power good pin. Such feature may be applied in a generic manner to existing power controller chips, such as the ISL6227, ISL6269 and ISL6260 chips manufactured by Intersil Corporation, the MAX1999 manufactured by Maxim Integrated Products, Inc., the SC1486 manufactured by Semtech Corporation, among other power management controllers.